1. The Field of the Invention
The present invention relates generally to high speed data transmission systems. More particularly, the present invention relates to a single layer flexible circuit.
2. The Related Technology
Fiber-optics and optoelectronics are important aspects of modern networking circuits because they allow for efficient, accurate and rapid transmission of data between various components in the network system. As with the design of most systems, design considerations often determine the extent of use of a fiber optic system. For example, the size and modularity of components or devices must often be balanced against the need for additional space to accommodate heat dissipation and circuit monitoring components. While it is desirable to minimize the size of the component, some design considerations have previously limited this minimization due to their inherent characteristics. For example, some optoelectronic components generate large amounts of heat which become more difficult to dissipate as the size of the component becomes smaller. Further, as the component becomes smaller, there is less space available for mounting and connecting additional components thereto.
Modular components are desirable in fiber optic systems to reduce the cost of manufacturing the system, which cost increases the more customized the system becomes. An example of a modular component is a transceiver. Transceivers usually include an input receiver optical subassembly (ROSA) and an output transmitter optical subassembly (TOSA). The ROSA comprises a photodiode for detecting optical signals and sensing circuitry for converting the optical signals to digital signals compatible with other network components. The TOSA comprises a laser for transmitting optical signals and control circuitry for modulating the laser according to an input digital data signal. The TOSA has an optical lens for collimating the light signals from the laser of the TOSA to an optical fiber. Additionally, the transceiver includes pluggable receptacles for optically connecting the TOSA and the ROSA with other components within a fiber optic network. The transceiver often includes an electronic connector for connection to electrical components of a host system that has a computer or communication device with which the transceiver operates.
The design of the transceiver, as well as that of other modular components within the fiber optic system, is preferably standards-based, such that components can be connected without significant customization. Typically, standards define various characteristics such as size, power consumption, and connector configuration. When designing components to operate within a particular standard, attention must be given to what components are selected and how they are configured so as to not exceed the rated power consumption. These components are constrained by principles of semiconductor physics to work preferentially in a certain temperature range. Factors such as power dissipation, size and materials uniquely determine the operating temperature of the component for given ambient conditions, such as ambient temperature, and airflow. The resulting operating temperature determines the types of optical and electronic devices that can be successfully operated within the component.
The photodiode in the ROSA and the laser in the TOSA are examples of optoelectronic components. Generally, these optoelectronic components are sensitive electrical devices which require protection. As such, these optoelectronic components are usually manufactured in packaging assemblies. One such packaging assembly is known as a transistor-outline header or transistor-outline package, referred to herein as a TO package or TO can. TO packages are widely used in the field of optoelectronics, and may be employed in a variety of applications. As such, TO packages are often standardized to facilitate their incorporation into components such as transceivers. The TO packages protect the sensitive electrical devices contained therein and electrically connect such devices to external components such as printed circuit boards (“PCB”).
With respect to their construction, the TO packages often include a cylindrical metallic base with a number of conductive leads extending completely through, and generally perpendicular to, the base. The size of the base is often sized to fit within a specific TO standard size and lead configuration, examples of which include a TO-5 or TO-46. The leads are usually hermetically sealed in the base to provide mechanical and environmental protection for the components contained in the TO package, and to electrically isolate the conductive leads from the metallic material of the base. Typically, one of the conductive leads is a ground lead that may be electrically connected directly to the base.
Various types of electrical devices are mounted on one side of the base and connected to the leads. Generally, a cap is used to enclose the side of the base where such electrical devices are mounted, so as to form a chamber that helps prevent contamination or damage to those electrical device(s). The design of the TO package depends on the optoelectronic component being mounted on the base and the modular component to which the TO package will be used. By way of example, in applications where the optoelectronic component mounted on the base is an optical component, the cap is at least partially transparent so to allow an optical signal generated or received by the optical component to be transmitted to or from the TO package. These optical TO packages are also known as window cans.
Problems may arise when connecting the TO package to other components of the circuitry. TO packages have conventionally been connected to a PCB using through-hole technology. That is, vias or holes are drilled through the PCB corresponding to each lead. The base of the TO package is placed parallel to the PCB and the leads are then disposed through the vias and welded, soldered or otherwise connected to the PCB.
However, the conductive lead configuration of a conventional TO package complicates how the package, and ultimately, the modular component to which it is associated, is connected to other components of the system, such as, for example, the PCB. Where it is desirable to position the TO package in any other orientation, the TO packages do not connect as easily to the PCB. The TO package can be positioned on its side such that the base is perpendicular to the PCB. This configuration may be desirable where the optic window is disposed at the top of the package and the incoming or outgoing optical signal is coming from the side (such as in a side-emitting configuration). In this arrangement, the leads of the TO package straddle the outer edge of the PCB such that some of the leads are on the top surface of the PCB and some of the leads are on the bottom surface of the PCB. The leads are then bonded to the PCB and the ends of the leads may be further reinforced using a solder paste. The cap portion of the TO package may be at least partially disposed in a TOSA/ROSA port to form a TOSA/ROSA subassembly which is connected to the housing or chassis of the electronic unit.
In this configuration, the separation or pitch of the leads exiting the TO package and the thickness of the PCB can vary. To form a strong solder joint, the leads should rest on the solder pads of the PCB. Frequently, because of this mis-match between the lead pitch and the thickness of the PCB, the leads must be bent into a flattened “s” shape so they will lie parallel and against the pads of the PCB. This requires either very specialized tooling or manual lead forming by operators. If done manually, the lead forming is frequently imperfect and irregular and the resulting solder joint can be of poor quality. The glass-to-metal seal on the TO package is also subject to cracking and damage from lead forming operations. In addition, the special lead forming operation of this configuration adds extra assembly cost.
This configuration can further be undesirable because the leads are unsupported between the base and the PCB and thus unable to withstand torque, gravitational, or other pressure or jostling which may be applied to the leads during normal use of the electronic unit. For example, the solder pads on the PCB to which the leads are connected are not anchored to the PCB by anything more than just the adhesion of the pad. Thus, the solder pads can become dislodged from the PCB. Further, while solder joints may be applied between the leads and the PCB, the solder joint is not strong, and it could potentially crack or fail. In addition, the other end of the PCB is configured to connect to an edge connector member. When the TO package is connected to the PCB using straddle mounting, the whole structure is rigid so that any stress applied to any part of the structure transfers stress to the solder joint. The foregoing configuration thus presents a module in which failure is likely.
In light of the above discussion, a need exists for a scheme by which leads of an optoelectronic component can be connected to another component, such as a printed circuit board, while avoiding the problems and challenges described above.